The invention relates to a method and device for controlling a displaceable object operated by a motorized drive unit, for example a window pane, a sliding roof or the like in a motor vehicle. It is especially suitable for use as a collision protector, for example, to prevent objects from becoming trapped between the vehicle frame and the window pane as it is being closed. It also allows simplified attachment of a transmitter and receiver on the displaceable object.
From DE 42 15 744 A1 a device is known for controlling remote-controlled parts, such as, for example, a window pane in a vehicle, which produce acoustic surface waves (so-called Rayleigh waves) by means of an electrical-mechanical converter (actuator), designed as a sensor, on an edge of the displaceable part, such as, for example, a window pane. This edge is in wave-conducting connection with the edge of the area being monitored, for example the closing area of the window pane. A receiver on the other side of the area being monitored measures the energy of the incoming surface waves and sends the measured signals to an electronic evaluator unit.
It is also proposed to use only a one-piece transmitter/receiver unit, or wedge converter, wherein at an opposite end of the area being monitored there is a reflector, for example a notch in the pane edge, which is suitable to reflect a sufficiently large part of the emitted surface wave energy so that a measured signal is generated in the transmitter/receiver unit which is capable of being evaluated. As a result of a signal damping detected from the area being monitored and measurable on the receiver through dissipation of the surface wave energy on contact with area being monitored, conclusions are drawn regarding a possible case of collision, and the direction of movement of the displaceable part is reversed, where applicable, in the "opening" direction.
The wedge converters required for surface wave generation and receiving described in the above-mentioned reference have however the disadvantage that their attachment on the edge of the displaceable object is not quite straightforward since the propagation direction characteristics of the surface waves have to be observed absolutely. Thus, a wedge converter can only produce surface waves in one propagation direction or receive them from one propagation direction. There is also the drawback that the use of the inventive principle on the basis of wedge converters for reasons of space requires that they are fixed solely outside of the visible area of the edge (of the displaceable object). When monitoring side window panes, this means that the wedge converters are attached to the lower edge of the window pane. The area of the edge of the displaceable object on which the converters are fixed can be locally separated from the monitoring area by a seal which likewise has a damping effect. The damping effect of the seal can however under certain circumstances lead to faulty interpretations of the measured results.
As an alternative to wedge converters it is possible to use shear vibrators or interdigital converters. These can be fixed directly on the edge of the area to be monitored. The manufacture of such converters is however substantially more expensive than manufacturing thickness vibrators.